Kako sam kreirao React aplikaciju na jednoj stranici

Programiranje

S strukturama podataka, komponentama i integracijom s Reduxom

Nedavno sam izradio aplikaciju na jednoj stranici koja komunicira s pozadinskim JSON API poslužiteljem. Odlučio sam koristiti React kako bih produbio svoje razumijevanje osnova React-a i kako svaki alat može pomoći u izgradnji skalabilne frontend-a.

Niz ove aplikacije sastoji se od:

  • Sučelja s React / Redux
  • Zaštitni JSON API poslužitelj sa Sinatrom, integriran s Postgresom za trajnost baze podataka
  • API klijent koji dohvaća podatke iz OMDb API-ja, napisanog na Ruby

Za ovaj ćemo post pretpostaviti da smo dovršili pozadinu. Dakle, usredotočimo se na to kako se donose odluke o dizajnu izvana.

Napomena: Ovdje predstavljene odluke samo su informativne i mogu se razlikovati ovisno o potrebama vaše prijave. Ovdje se za demonstraciju koristi primjer OMDb Movie Tracker aplikacije.

Aplikacija

Aplikacija se sastoji od obrasca za unos pretraživanja. Korisnik može unijeti naslov filma za povratak rezultata filma s OMDb-a. Korisnik također može spremiti film s ocjenom i kratkim komentarom na popis favorita.

Da biste pogledali konačnu aplikaciju, kliknite ovdje. Da biste pogledali izvorni kod, kliknite ovdje.

Kada korisnik pretražuje film na početnoj stranici, to izgleda ovako:

Radi jednostavnosti, u ovom ćemo se članku usredotočiti samo na osmišljavanje osnovnih značajki aplikacije. Također možete preskočiti na II. Dio: Reduxserije.

Struktura podataka

Definiranje odgovarajućih struktura podataka trebao bi biti jedan od najvažnijih aspekata dizajniranja aplikacije. To bi trebao biti prvi korak, jer određuje ne samo kako frontend treba generirati elemente, već i kako API poslužitelj treba vratiti JSON odgovore.

Za ovu aplikaciju trebat će nam dvije glavne informacije za pravilno prikazivanje našeg korisničkog sučelja: rezultat jednog filma i popis omiljenih filmova .

Objekt rezultata filma

Rezultat jednog filma sadržavat će informacije kao što su naslov, godina, opis i slika postera. Ovim moramo definirati objekt koji može pohraniti ove atribute:

{ "title": "Star Wars: Episode IV - A New Hope", "year": "1977", "plot": "Luke Skywalker joins forces with a Jedi Knight...", "poster": "//m.media-amazon.com/path/to/poster.jpg", "imdbID": "tt0076759"}

posterNekretnina je jednostavno URL poster sliku koja će se prikazati u rezultatima. Ako za taj film nema plakata, bit će "N / A", a mi ćemo prikazati rezervirano mjesto. Trebat će nam i imdbIDatribut za jedinstvenu identifikaciju svakog filma. Ovo je korisno za utvrđivanje postoji li filmski rezultat već na popisu omiljenih. Kasnije ćemo istražiti kako to funkcionira.

Popis favorita

Popis omiljenih sadržavat će sve filmove spremljene kao omiljene. Popis će izgledati otprilike ovako:

[ { title: "Star Wars", year: "1977", ..., rating: 4 }, { title: "Avatar", year: "2009", ..., rating: 5 }]

Imajte na umu da ćemo s popisa trebati potražiti određeni film, a vremenska složenost ovog pristupa je O (N) . Iako dobro funkcionira za manje skupove podataka, zamislite da biste morali tražiti film na popisu omiljenih koji raste u nedogled.

Imajući ovo na umu, odlučio sam ići s hash tablicom s ključevima kao imdbIDi vrijednostima kao omiljeni filmski objekti:

{ tt0076759: { title: "Star Wars: Episode IV - A New Hope", year: "1977", plot: "...", poster: "...", rating: "4", comment: "May the force be with you!", }, tt0499549: { title: "Avatar", year: "2009", plot: "...", poster: "...", rating: "5", comment: "Favorite movie!", }}

Pomoću toga možemo film potražiti na popisu omiljenih u O (1) vremenu prema njegovim imdbID.

Napomena: složenost izvođenja vjerojatno u većini slučajeva neće biti bitna, jer su skupovi podataka obično mali na strani klijenta. Ionako ćemo također izvršiti rezanje i kopiranje (također O (N) operacije) u Reduxu. Ali kao inženjer, dobro je biti svjestan potencijalnih optimizacija koje možemo izvršiti.

Komponente

Komponente su u središtu Reacta. Morat ćemo odrediti koji će komunicirati s trgovinom Redux, a koji samo za prezentaciju. Također možemo ponovno upotrijebiti neke prezentacijske komponente. Naša hijerarhija komponenata izgledat će otprilike ovako:

Glavna stranica

Svoju komponentu aplikacije označavamo na najvišoj razini. Kada se posjeti korijenska staza, treba prikazati SearchContainer . Također treba prikazati flash poruke korisniku i rukovati usmjeravanjem na strani klijenta.

SearchContainer će preuzimanje rezultata film iz naše Redux trgovini, pružanje informacija rekvizite za MovieItem za renderiranje. Također će poslati akciju pretraživanja kada korisnik pošalje pretragu u SearchInputForm . O Reduxu više kasnije.

Dodaj u obrazac za favorite

Kada korisnik klikne na gumb "Dodaj u favorite", prikazat ćemo AddFavoriteForm , kontroliranu komponentu.

Stalno ažuriramo njegovo stanje kad god korisnik promijeni ocjenu ili unese tekst u području teksta komentara. Ovo je korisno za provjeru valjanosti nakon podnošenja obrasca.

Obrazac za ocjenu odgovoran je za prikazivanje žutih zvjezdica kada ih korisnik klikne. Također izvještava o trenutnoj vrijednosti ocjene za AddFavoriteForm .

Kartica Favoriti

Kada korisnik klikne na karticu "Favoriti", aplikacija prikazuje FavoritesContainer .

FavoritesContainer je odgovoran za dohvaćanje popisa favorita iz Redux trgovine. Također šalje radnje kada korisnik promijeni ocjenu ili klikne na gumb "Ukloni".

Our MovieItem and FavoritesInfo are simply presentational components that receive props from FavoritesContainer.

We’ll reuse the RatingForm component here. When a user clicks on a star in the RatingForm, the FavoritesContainer receives the rating value and dispatches an update rating action to the Redux store.

Redux Store

Our Redux store will include reducers that handle the search and favorites actions. Additionally, we’ll need to include a status reducer to track state changes when a user initiates an action. We’ll explore more on the status reducer later.

//store.js
import { createStore, combineReducers, applyMiddleware } from 'redux';import thunk from "redux-thunk";
import search from './reducers/searchReducer';import favorites from './reducers/favoritesReducer';import status from './reducers/statusReducer';
export default createStore( combineReducers({ search, favorites, status }), {}, applyMiddleware(thunk))

We’ll also apply the Redux Thunk middleware right away. We’ll go more into detail on that later. Now, let’s figure out how we manage the state changes when a user submits a search.

Search Reducer

When a user performs a search action, we want to update the store with a new search result via searchReducer. We can then render our components accordingly. The general flow of events looks like this:

We’ll treat “Get search result” as a black box for now. We’ll explore how that works later with Redux Thunk. Now, let’s implement the reducer function.

//searchReducer.js
const initialState = { "title": "", "year": "", "plot": "", "poster": "", "imdbID": "",}
export default (state = initialState, action) => { if (action.type === 'SEARCH_SUCCESS') { state = action.result; } return state;}

The initialState will represent the data structure defined earlier as a single movie result object. In the reducer function, we handle the action where a search is successful. If the action is triggered, we simply reassign the state to the new movie result object.

//searchActions.jsexport const searchSuccess = (result) => ({ type: 'SEARCH_SUCCESS', result});

We define an action called searchSuccess that takes in a single argument, the movie result object, and returns an action object of type “SEARCH_SUCCESS”. We will dispatch this action upon a successful search API call.

Redux Thunk: Search

Let’s explore how the “Get search result” from earlier works. First, we need to make a remote API call to our backend API server. When the request receives a successful JSON response, we’ll dispatch the searchSuccess action along with the payload to searchReducer.

Knowing that we’ll need to dispatch after an asynchronous call completes, we’ll make use of Redux Thunk. Thunk comes into play for making multiple dispatches or delaying a dispatch. With Thunk, our updated flow of events looks like this:

For this, we define a function that takes in a single argument title and serves as the initial search action. Thisfunction is responsible for fetching the search result and dispatching a searchSuccess action:

//searchActions.jsimport apiClient from '../apiClient';
...
export function search(title) { return (dispatch) => { apiClient.query(title) .then(response => { dispatch(searchSuccess(response.data)) }); }}

We’ve set up our API client beforehand, and you can read more about how I set up the API client here. The apiClient.query method simply performs an AJAX GET request to our backend server and returns a Promise with the response data.

We can then connect this function as an action dispatch to our SearchContainer component:

//SearchContainer.js
import React from 'react';import { connect } from 'react-redux';import { search } from '../actions/searchActions';
...
const mapStateToProps = (state) => ( { result: state.search, });
const mapDispatchToProps = (dispatch) => ( { search(title) { dispatch(search(title)) }, });
export default connect(mapStateToProps, mapDispatchToProps)(SearchContainer);

When a search request succeeds, our SearchContainer component will render the movie result:

Handling Other Search Statuses

Now we have our search action working properly and connected to our SearchContainer component, we’d like to handle other cases other than a successful search.

Search request pending

When a user submits a search, we’ll display a loading animation to indicate that the search request is pending:

Search request succeeds

If the search fails, we’ll display an appropriate error message to the user. This is useful to provide some context. A search failure could happen in cases where a movie title is not available, or our server is experiencing issues communicating with the OMDb API.

To handle different search statuses, we’ll need a way to store and update the current status along with any error messages.

Status Reducer

The statusReducer is responsible for tracking state changes whenever a user performs an action. The current state of an action can be represented by one of the three “statuses”:

  • Pending (when a user first initiates the action)
  • Success (when a request returns a successful response)
  • Error (when a request returns an error response)

With these statuses in place, we can render different UIs based on the current status of a given action type. In this case, we’ll focus on tracking the status of the search action.

We’ll start by implementing the statusReducer. For the initial state, we need to track the current search status and any errors:

// statusReducer.jsconst initialState = { search: '', // status of the current search searchError: '', // error message when a search fails}

Next, we need to define the reducer function. Whenever our SearchContainer dispatches a “SEARCH_[STATUS]” action, we will update the store by replacing the search and searchError properties.

// statusReducer.js
...
export default (state = initialState, action) => { const actionHandlers = { 'SEARCH_REQUEST': { search: 'PENDING', searchError: '', }, 'SEARCH_SUCCESS': { search: 'SUCCESS', searchError: '', }, 'SEARCH_FAILURE': { search: 'ERROR', searchError: action.error, }, } const propsToUpdate = actionHandlers[action.type]; state = Object.assign({}, state, propsToUpdate); return state;}

We use an actionHandlers hash table here since we are only replacing the state’s properties. Furthermore, it improves readability more than using if/else or case statements.

With our statusReducer in place, we can render the UI based on different search statuses. We will update our flow of events to this:

We now have additional searchRequest and searchFailure actions available to dispatch to the store:

//searchActions.js
export const searchRequest = () => ({ type: 'SEARCH_REQUEST'});
export const searchFailure = (error) => ({ type: 'SEARCH_FAILURE', error});

To update our search action, we will dispatch searchRequest immediately and will dispatch searchSuccess or searchFailure based on the eventual success or failure of the Promise returned by Axios:

//searchActions.js
...
export function search(title) { return (dispatch) => { dispatch(searchRequest());
apiClient.query(title) .then(response => { dispatch(searchSuccess(response.data)) }) .catch(error => { dispatch(searchFailure(error.response.data)) }); }}

We can now connect the search status state to our SearchContainer, passing it as a prop. Whenever our store receives the state changes, our SearchContainer renders a loading animation, an error message, or the search result:

//SearchContainer.js
...(imports omitted)
const SearchContainer = (props) => (   props.search(title) } /> { (props.searchStatus === 'SUCCESS') ?  : null } { (props.searchStatus === 'PENDING') ?    : null } { (props.searchStatus === 'ERROR') ?  
 { props.searchError } 
  : null } );
const mapStateToProps = (state) => ( { searchStatus: state.status.search, searchError: state.status.searchError, result: state.search, });
...

Favorites Reducer

We’ll need to handle CRUD actions performed by a user on the favorites list. Recalling from our API endpoints earlier, we’d like to allow users to perform the following actions and update our store accordingly:

  • Save a movie into the favorites list
  • Retrieve all favorited movies
  • Update a favorite’s rating
  • Delete a movie from the favorites list

To ensure that the reducer function is pure, we simply copy the old state into a new object together with any new properties usingObject.assign. Note that we only handle actions with types of _SUCCESS:

//favoritesReducer.js
export default (state = {}, action) => { switch (action.type) { case 'SAVE_FAVORITE_SUCCESS': state = Object.assign({}, state, action.favorite); break;
case 'GET_FAVORITES_SUCCESS': state = action.favorites; break;
case 'UPDATE_RATING_SUCCESS': state = Object.assign({}, state, action.favorite); break;
case 'DELETE_FAVORITE_SUCCESS': state = Object.assign({}, state); delete state[action.imdbID]; break;
default: return state; } return state;}

We’ll leave the initialState as an empty object. The reason is that if our initialState contains placeholder movie items, our app will render them immediately before waiting for the actual favorites list response from our backend API server.

From now on, each of the favorites action will follow a general flow of events illustrated below. The pattern is similar to the search action in the previous section, except right now we’ll skip handling any “PENDING” status.

Save Favorites Action

Take the save favorites action for example. The function makes an API call to with our apiClient and dispatches either a saveFavoriteSuccess or a saveFavoriteFailure action, depending on whether or not we receive a successful response:

//favoritesActions.jsimport apiClient from '../apiClient';
export const saveFavoriteSuccess = (favorite) => ({ type: 'SAVE_FAVORITE_SUCCESS', favorite});
export const saveFavoriteFailure = (error) => ({ type: 'SAVE_FAVORITE_FAILURE', error});
export function save(movie) { return (dispatch) => { apiClient.saveFavorite(movie) .then(res => { dispatch(saveFavoriteSuccess(res.data)) }) .catch(err => { dispatch(saveFavoriteFailure(err.response.data)) }); }}

We can now connect the save favorite action to AddFavoriteForm through React Redux.

To read more about how I handled the flow to display flash messages, click here.

Conclusion

Designing the frontend of an application requires some forethought, even when using a popular JavaScript library such as React. By thinking about how the data structures, components, APIs, and state management work as a whole, we can better anticipate edge cases and effectively fix errors when they arise. By using certain design patterns such as controlled components, Redux, and handling AJAX workflow using Thunk, we can streamline managing the flow of providing UI feedback to user actions. Ultimately, how we approach the design will have an impact on usability, clarity, and future scalability.

References

Fullstack React: The Complete Guide to ReactJS and Friends

About me

I am a software engineer located in NYC and co-creator of SpaceCraft. I have experience in designing single-page applications, synchronizing state between multiple clients, and deploying scalable applications with Docker.

I am currently looking for my next full-time opportunity! Please get in touch if you think that I will be a good fit for your team.